Field
Implementations of the present disclosure generally relate to methods and apparatus for forming a film on a substrate. More particularly, implementations of the present disclosure relate to methods and apparatus for heteroepitaxial growth of crystalline films.
Description of the Related Art
Group III-V and Group II-IV compounds are finding greater importance in the development and fabrication of a variety of semiconductor devices, such as, for example, complementary metal-oxide semiconductors (CMOS), light emitting diodes (LEDs), laser diodes (LDs) and logic circuit devices such as field effect transistors (FETs). In these devices, a plurality of semiconductor layers having different mixed crystal compositions are layered together to obtain intended optical and electrical characteristics.
Group III-V and Group IV compound films are generally formed by heteroepitaxy, a form of epitaxy. In epitaxy, a monocrystalline film is deposited on a monocrystalline substrate from gaseous or liquid precursors. During deposition, the substrate acts as a seed crystal, the deposited film takes on a lattice structure and orientation identical to those of the substrate. The deposited film is typically referred to as an epitaxial film or epitaxial layer. In heteroepitaxy, the epitaxial film and the substrate typically include different materials having different properties, for example, lattice constant and thermal expansion coefficient. The differences in properties introduce defects in the epitaxial film and may even cause the substrates to crack when growing high crystalline nitrides. For example, when growing gallium nitride material on a silicon substrate, mechanical stress and thermal stress are generated due to difference in lattice constants and thermal expansion coefficients causing the silicon substrate to bow and the gallium nitride film and even the silicon substrate to crack.
One approach to reducing the defect density involves growing thick strain relaxed buffer (SRB) layers on the substrate. These thick SRB layers that may be targeted for strain relaxation can be expensive to grow. Others have attempted to grow dissimilar materials that have a tendency to relax quickly on the substrate of choice, or otherwise grow thicker films that eventually relax due to accumulated strain. However, these processes often take a long time to complete and involve costly materials. Thus, there is a need for thinner strain relaxed buffer layers that reduce defect density while reducing processing times and costs. However, these thinner buffer layers often suffer from morphological defects after being exposed to subsequent annealing processes.
Therefore, there is a need for methods for depositing thin strain relaxed buffer layers that maintain smooth surface morphology after exposure to subsequent annealing processes.